Evaluation of Potential Essential Oils against Postharvest Rot of Apple

Apple (Malus domestica) fruits after harvest, especially when stored for a longer period, are found to be susceptible to postharvest rots present study as conducted to find out the pathogens that result the postharvest rot in apples and the positional use for essential oils as an alternative of  fungicides. For this purpose, local fruit market of Hyderabad was visited for the collection of specimens. Apple fruit showing postharvest rot was collected and brought to the laboratory of Plant Pathology for isolation of associated pathogens. Isolation was done on PDA medium, using the tissue isolation method. The most predominantly isolated pathogen was identified as Aspergillus niger, which was isolated from 76.25% of the rotted tissues used for the isolation. Other pathogens that were isolated were Colletotrichum spp. Penicillum sp, and Rhizopus stolonifera, were isolated with frequency of 13.75, 6.25 and 3.75 % respectively. Etiology of the most predominantly isolated pathogen. i.e., A. niger, was confirmed. For this purpose, harvested apple fruits were inoculated by the standard method, by placing the culture disk of A. niger. Un-inoculated fruits served as control. Fruits were stored in the laboratory for symptom development in disposable boxes. After incubation rotting was noticed to start after 4th day and spread very quickly during storage after infestation. Mean disease severity as the average diameter of the rotted area in relation to the total area of the fruit after 20 days of inoculation was 42% in inoculated fruits. Whereas very small rot development (6%) was observed in control (un-inoculated). Identical symptoms as observed from naturally infested fruits were developed. The affected portion showed yellowish brown to dark brown, circular discoloration and was soft in nature. Lesions appear at the point of an incision made in an apple, and as the rot spreads throughout the apple. Management actions that include using antifungal qualities of essential oils are exploited using eleven essential oils viz., Clove, Kalonji, Lemon, Orange, Eucalyptus, Tea, Citronella, Rosemary, Lemon grass, Peppermint, and Jasmine. These essential oils were evaluated against the causal agent (Aspergillus niger) of fruit rot of apples under in-vitro conditions by using the food poisoning method with four different concentrations (0.25, 0.50, 0.75 and 1% V/V). Aspergillus niger appeared sensitive to all the used essential oil. Lemon, Clove, Tea, Citronella, Rosemary, Lemon grass, Peppermint, and Jasmine appeared as highly effective, as even the lowest used dose of 0.25 % completely inhibited (100%) the growth of the pathogen. The growth response of A. niger to the used concentration of Kalonji, Orange and Eucalyptus essential oils varied greatly within the different treatments and doses. Next, the essential oil of clove and lemon were checked for their potential against postharvest rot development in apple fruits inoculated with A. niger. For this purpose apple fruits were inoculated with pathogens and after 24 hours treated with essential oil by dipping in essential oil suspension (water+ essential oil+ drop of tween 20). Un-treated but inoculated fruits served as control. Final data on lesion development was recorded after 20 days of incubation. Essential oil significantly reduced disease development. in un-treated fruit average lesion area was measured as 40.17%. Whereas’s a very slight rot (1.67 %) was recorded in treated fruits. The present study confirms that essential oil treatments are beneficial against postharvest fungal infections; however, the efficiency of these treatments may vary depending on the fruit cultivar, essential oil composition and concentration, and storage length.